> How would you access individual characters of a string in the 
> preprocessor?

Indeed, the preprocessor can't look 'inside' a string literal.

The only technique I can think of that would work would be something like:

*** WARNING: Untested code ***

#define H(partial,c) ((partial) << 1) ^ (c)

unsigned int hash(char const *p)
{
    unsigned partial=0;
    while ( *p )
    {
        paritial <<= 1;
        partial ^= *p;
        ++p;
    }
}

....

char *p;
switch hash(p)
{
    case H(H(H(0,'a'),'b'),'c') :
        DoSomething();
        break;
    case H(H(H(H(0,'d'),'e'),'f''),'g'):
        DoSomethingElse();
        break;
    default:
        UnknownCommand();
}

-----

you could define macros like:

#define H1(a) H(0,(a))
#define H2(a,b) H(H1(a),(b))
#define H3(a,b,c) H(H2(a,b),(c))
#define H4(a,b,c,d) H(H3(a,b,c),(d))

then your cases would be:

    case H3('a','b','c'):
        ..
    case H4('d','e','f','g'):

-----

--- Bob Ammerman
RAm Systems


-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist